The configuration of most rotational viscometers requires a rotating element called the rotor and a stationary element called the stator, which contains the fluid to be tested for properties such as viscosity, and in which most typically the rotor rotates in contact with the fluid so as to determine drag caused by the fluid. This drag can then be related to the viscosity of the fluid.
Rotational viscometers such as the Brookfield viscometer are well-known instruments for measuring viscosities of liquids. Usually, the rotor, which is driven by a motor in the Brookfield head or module, is immersed in a large container of liquid in which the walls of the container are at some considerable distance from the rotor and thus have little influence on the measurement of the viscous value. This container is the stator. In some applications such as in the well-known Scanning Brookfield Technique, discovered and developed by Mr. Theodore W. Selby and licensed to the Tannas Co., Midland, Mich., and used in ASTM D 5133, incorporated herein by reference as its 1990 version, the rotor must be relatively close to the stator wall to gain the necessary sensitivity. In such a case, the rotor must be centered carefully.
Typically, the stator is fixed to the Brookfield module by means of a stator collar. See e.g., Deysarkar et al., U.S. Pat. No. 4,648,263 (Mar. 10, 1987).
In practice, problems are encountered with the commercially available support and centering attachment as of Deysarkar et al., which is known commercially as the Pennzoil/Tannas rotor/stator centering adapter, Tannas Model Number SBV-P. In particular, and in reference to the foregoing patent, an O-ring, present in the SBV-P adapter in a slot cut in interior surface 54 of cylindrical member 70, can swell as from contact with solvents or oil to the point where sometimes, upon the contraction of the constraining cylindrical member 70, a glass stator 28 may be difficult to remove or actually break in removal. The O-ring also may become worn or oily, and, if a loose fit between cylinder member 70 and stator 28 is engendered, slippage and rotation of the stator occurs during testing, which destroys the value of the test. Furthermore, the O-ring can be difficult to install and remove for replacement. Another effect of low-temperature contraction of cylindrical member 70 is that when bath 44 controls the test liquid temperature at minus forty degrees C., or below, separation of parts of device 40, to include removal of a glass stator 28, filled with tested liquid, from the lower end 52 of the device, becomes very difficult because of the aforementioned contraction of the engineering thermoplastic employed to make the adapter.
A further problem in low-temperature viscometry is the need to introduce dry air or gas above the liquid being cooled so that the surface of the oil does not gather moisture and form ice.
Accordingly, research has been directed at solving such problems at the Tannas Co. Note in this connection the following U.S. patent applications: Van Meter et al., Ser. No. 08/308,918, filed on Sep. 20, 1994, U.S. Pat. No. 5,513,517 (May 7, 1996), entitled ROTOR-STATOR ADAPTER FOR SENSITIVE ROTATING VISCOMETERS; Van Meter, Ser. No. 08/336,379, filed on Nov. 8, 1994, U.S. Pat. No. 5,517,850 (May 21, 1996) entitled ROTOR-STATOR ADAPTERS WITH INTERNALLY THREADED STATOR COLLAR & EXTERNALLY THREADED NUT FOR SENSITIVE ROTATING VISCOMETERS. See also, Van Meter et al., design Ser. No. 29/030,792, filed on Nov. 8, 1994, entitled COLLAR HOUSING FOR A ROTOR-STATOR ADAPTOR FOR SENSITIVE ROTATING VISCOMETERS, which issued on Nov. 21, 1995 as Des. 364,351. Each of these inventions involves a stator collar, improvements over the support and centering device of Deysarkar et al., and the commercial model SBV-P.
However, manufacture and commercialization of such adapters or stator collars is, in general, not without noteworthy expense. Moreover, the requirement of an adapter or stator collar can present an additional investment in operator training, and equipment upkeep.
What is needed is an arrangement or article which overcomes such problems or hurdles, while providing for precise centering of the rotor spindle in the stator of a sensitive rotating viscometer. It should be readily manufacturable and commercializable--and be efficient to operate, especially by inexperienced operators.